1. Field of the Invention
The present invention relates to a dielectric capacitor and a memory, which are supported by a substrate portion and in which a first electrode, a dielectric film and a second electrode are formed successively on the substrate portion and a method for manufacturing the same.
2. Description of the Related Art
A ferroelectric memory is a rapidly rewrittable, non-volatile memory by means of rapid polarization inversion and its residual polarization of a ferroelectric film. Conventionally, as the ferroelectric memory, a memory in which a dielectric capacitor and a transistor are arranged in parallel with the direction along which a base surface extends is known, for example. In such a ferroelectric memory, for example, the dielectric capacitor has a construction in which an adhesive layer made of titanium (Ti), a bottom electrode layer made of platinum (Pt), a ferroelectric film made of a bismuth (Bi) inclusion layer structure oxide or PZT which is a solid solution of PbTiO.sub.3 and PbZrO.sub.3, and a top electrode layer made of platinum are stacked successively on a base sandwiching an insulating layer in between.
Further, in order to increase information recording density, a so-called stack type capacitor in which a transistor and a ferroelectric capacitor are stacked on the base is known. In the ferroelectric memory, for example, the transistor and the bottom electrode of the ferroelectric capacitor are electrically coupled through a plug layer made of silicon (Si) and also an anti-diffusion layer for preventing diffusion of a chemical element on the bottom electrode of the ferroelectric capacitor is provided. The anti-diffusion layer is for preventing conductivity of the bottom electrode from being lost when silicon is diffused from the plug layer onto the bottom electrode and oxidized in the top layer portion. The anti-diffusion layer is also for preventing a capacitor characteristic from being deteriorated significantly when the silicon is diffused onto the ferroelectric film. Both are caused by thermal annealing at a high temperature as approximately 600-800.degree. C. in forming the ferroelectric film. As such a ferroelectric memory, for example, the anti-diffusion layer including iridium (Ir), hafnium (Hf), and oxygen (O), which is formed on the bottom electrode has been conventionally reported (Refer to Japanese Unexamined Patent Application Publication No. Hei 10-242409.)
However, in the conventional ferroelectric capacitor, since platinum is used as an electrode material, a problem exists such that micromachining is difficult. Thus, there is a need for use of another electrode material which is easy to process. However, since the top electrode is particularly formed in such a manner that a bottom electrode, a ferroelectric film and a top electrode are sequentially stacked on a substrate, it gives a great influence on the bottom electrode and the dielectric film in the manufacturing process. In another words, requirements are needed for the electrode material, but the conventional material is not satisfactory in this respect.
For example, when precious metal other than platinum or gold (Au) is used for the bottom electrode including the anti-diffusion layer, the characteristics of the ferroelectric film deteriorate due to hydrogen annealing for recovering the functionality of the transistor. It is considered that this deterioration is influenced by the hydrogen annealing which reduces precious metal oxide produced at the time of forming the ferroelectric film. In order to prevent the deterioration, it may be effective that the precious metal oxide produced at the time of forming ferroelectric film is reduced before the hydrogen annealing. Thus, a material which can obtain a great characteristic by heat processing in an inert-gas atmosphere is desired for comprising the top electrode.
Further, conventionally, a ferroelectric capacitor is formed by depositing the top electrode after crystals of the ferroelectric film have sufficiently grown and then processing by etching. However, in many cases, the pure reactive ion etching (RIE) method can not be applied for the top electrode and the ferroelectric film, and therefore sputter etching also takes place in the etching processing. In that case, if the surface roughness is large, the surface roughness is transferred to the substrate. Thus, desirably the etching takes place when the surface condition is still favorable before the crystals of the ferroelectric film have grown. For the top electrode, required is a material which can obtain favorable characteristics even when the top electrode is deposited and crystals are grown before crystals of the ferroelectric film are grown. Among conventional electrode materials, only platinum can be used for depositing the top electrode and causing the crystals to be grown in a condition where crystallinity of the ferroelectric film is low. However, the ferroelectric capacitor manufactured in this method is shorted completely by the hydrogen annealing for recovering the functionality of the transistor. Therefore, it is difficult to put it into practical use.